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Discussion Starter · #1 ·
Sorry to bring up the same old EGR issue. I have an 04 3 litre GU with 160,000kms. Have a 'Fat Pipes' 2 1/2 free flowing exhaust, catch can and intercooler fan. Goes great. Not one problem.

Would like to block EGR. Have found a mob that will do it for me and put on dyno. They say if the turbo is adjusted properly I will not need a Dawes valve as they can adjust turbo on dyno not to over boost.
I have a boost and EGT guage and to date have never seen boost over 14psi.

I replaced MAF at 120,00 and clean it with MAF cleaner every 20,000 kms. I tow a 19ft van.

Question is- Do I need a Dawes valve or is this guy right in that he can adjust turbo to stop overboosting.

Thanks heaps.
 

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Atleast one and a needle valve

The problem I have with blocking the EGR on a ZD without putting in a dawes/needle is not overboost (Id consider that to be above 20psi) but the ECU ordered drop in boost pressure when cruising (Ie EGR conditions) that will result in the donk running rich and hence high EGTs.

And pull the intake manifold off and clean out the EGR gunk, bloody useless doing everything else without doing this very very important step.
 

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Mate with my 07 3.0lt wagon I fitted my new exhaust and blocked off my EGR prior to fitting my pyro and boost gauge. In doing that it created an overboost problem and the vehical developed a surging issue and I was unable to see what the boost was doing. After reading many threads and the GU reference manual on here I figured the easiest way to lower my boost level was to adjust my VNT screw on the turbo. I did this by the required amount and the suging issue disappeared. Now that I've got my gauges fitted I've found that my boost only ever reaches 16 PSI max so I guess I was just arsey when I did the adjustment so my answer to you is 'No you shouldn't need a Dawes valve'.
Oh if you don't mind me asking who's the mob that'll do it for you as I had some work done by 4DT in bundy and they're not bad...
Let us know the outcome..

Cheers
Damien
 

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Grenade Master
GU4 05
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They say if the turbo is adjusted properly I will not need a Dawes valve as they can adjust turbo on dyno not to over boost.
I have a boost and EGT guage and to date have never seen boost over 14psi.
Thanks heaps.
I'd certainly install Dawes valve as it is cheap and effective insurance, in you case the hardest step in the Dawes valve installation is already done. Just "Tee-off" of the existing boost gauge fitting/line.
I also recommend NOT to fiddle with turbo VGT stop screw, use Dawes/needle valve/s for boost control/limiting instead. Also Benno's advice is correct as well, clean up the intake manifold too. It will be an eye opener for sure. Cheers
 

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Go Hard or Go Home
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I'd certainly install Dawes valve as it is cheap and effective insurance, in you case the hardest step in the Dawes valve installation is already done. Just "Tee-off" of the existing boost gauge fitting/line.
I also recommend NOT to fiddle with turbo VGT stop screw, use Dawes/needle valve/s for boost control/limiting instead. Also Benno's advice is correct as well, clean up the intake manifold too. It will be an eye opener for sure. Cheers
Care to explain as to why you do not recommend adjusting the grub screw to limit boost?

Its a far cheaper option if overboost symptoms are evident.
 

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ZD30 Out - L77 In!
nissan patrol
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Atleast one and a needle valve

The problem I have with blocking the EGR on a ZD without putting in a dawes/needle is not overboost (Id consider that to be above 20psi) but the ECU ordered drop in boost pressure when cruising (Ie EGR conditions) that will result in the donk running rich and hence high EGTs.

And pull the intake manifold off and clean out the EGR gunk, bloody useless doing everything else without doing this very very important step.
X2,

As well as limiting boost, the main reason for using a Dawes valve is to have manual control rather than having erratic boost control from the ECU. The ECU will always raise and lower boost when delivering EGR. If you block the EGR, it’s better to remove ECU boost control and allow the turbo to work like a conventional one, supplying constant boost. By fitting a Dawes valve controller, you can have constant boost at lower levels and lower EGT’s at the same time without sacrificing power.
 

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Nissan GUII 3L Patrol
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I blocked my egr without a Dawes valve and ran like this for about 4 months ( Dawes now installed ) the biggest issue I faced was the random boost changes on the highway, the boost would fluctuate depending on slight throttle inputs..between 6psi and 20psi ( this was with the vnt screw adjustments ) this also created large fluctuations in egr temps. The car ran fine... And around town it was not an issue, that all being said I now have a Dawes valve and the boost no longer fluctuates as much and Egrs are far steadier. Boost is now limited to about 16psi and highway temps rarely het over 400-450.
My next step is the dual Dawes with in cab needle valve like some of the other guys are running.

The Dawes valve is cheap and easy to fit so well worth it IMO.
 

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Grenade Master
GU4 05
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Care to explain as to why you do not recommend adjusting the grub screw to limit boost?

Its a far cheaper option if overboost symptoms are evident.
Perhaps it is but it is not the right way IMHO.
I believe that playing with the adjusting screw to lower a boost can result in either slowing down the boost pressure rise which in turn reduces the response (the last thing I want is waiting for things to happen when planting the right foot down) or if doing it wrong way can cause a boost surge at lower revs which can cause a turbo failure. Now considering that it ain't easy to fiddle with either just adjusting the screw to see what happens is a wrong way to go about it. If one has an access to engine dyno tune than that is possibly an option to do in order of fine tuning the performance. That is mine 2 cents worth in the debate.
 

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builder not a buyer!
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Adjusting the vnt grub, from what I have been led to believe, has no effect on your maximum boost as the ecu is still in control. The grub screw controls the spool rate afaik. Correct me if I'm wrong.

IMO I would fit the Dawes and needle valve. It gave me piece of mind to know exactly what was happening when driving the goonie. It becomes very predictive which makes driving it harder alot easier as I know how the engine will react when I sink the boot. Also the above advantages of lowering egts. I did the egr block before the Dawes setup and am much happier with the way it performs and will be happy to see better economy once the ecu re learns the new setup.

Cheap peace of mind, my 2 pennys worth

good luck
 

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Adjusting the vnt grub, from what I have been led to believe, has no effect on your maximum boost as the ecu is still in control. The grub screw controls the spool rate afaik. Correct me if I'm wrong.
Consider yourself corrected chuckles but you are still half right :) - lowering the grub will affect the spool rate but it also in turn limits / lowers the max boost as well.

Cheers,
Whitie
 

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Go Hard or Go Home
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Fair point rumcajs

Perhaps it is but it is not the right way IMHO.
I believe that playing with the adjusting screw to lower a boost can result in either slowing down the boost pressure rise which in turn reduces the response (the last thing I want is waiting for things to happen when planting the right foot down) or if doing it wrong way can cause a boost surge at lower revs which can cause a turbo failure. Now considering that it ain't easy to fiddle with either just adjusting the screw to see what happens is a wrong way to go about it. If one has an access to engine dyno tune than that is possibly an option to do in order of fine tuning the performance. That is mine 2 cents worth in the debate.
If people follow the reference doc and have a boost gauge, I think they will be ok in setting the max boost.

While I have the Dawes fitted (was fitted prior to me purchasing the vehicle), I think it is fantastic. As already stated, it takes away the control from the ECU.

With my rig a 6 month 2003 with all the mods, it is useless without the Dawes fitted. It suffered overboost all the time, low boost when cruising at 100km/hr and this is why the previous owner set it up with the Dawes and needle valve and took control away from the ECU.

My point was more for some one who was satisfied with the boost being controlled correctly by the ECU and not overboosting until the EGR mod. If a simple adjustment from the grub screw controls the over boost, then why not.

However if boost is not being controlled correctly by the ECU, then add the Dawes & needle valve.
 

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Benno wrote:
"that will result in the donk running rich and hence high EGTs."

That would not be correct if everything is working as it should. The ECU adjusts fuel according to airflow, running lower boost will reduce power, but it will not cause the engine to run rich.

I have had a dawes valve and took it out again because it increased my fuel consumption by about a litre per hundred km.
The truck certainly was nicer to drive with it, but I was also a bit concerned about the fast spool up (which could be corrected with a needle valve), but I didn't want to fit another gadget.
I also monitored the vacuum solenoid and noticed that it rarely lets the turbo work with the vanes fully closed, so I thought it was better to put up with a bit of boost fluctuations and get the lower fuel consumption.
The other issue I had was losing clutch vacuum really fast, which does not happen with the standard setup (not an issue with autos).
 

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Currently in PAD rehab
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My boost controller should be here soon from 3barracing.. im looking forward to getting this and the needle valve (which i got from dependable distributors), and the EGT and boost gauges plumbed in.

Can anyone recommend someone in Adelaide to tap my boost thingy into the shuzbucket, and weld in the 1/8 EGT thingo into the dump pipe? PM me :)

Will replace the dump pipe when i can save up for an exhaust upgrade, but that wont be till next year...
 

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Benno wrote:
"that will result in the donk running rich and hence high EGTs."

That would not be correct if everything is working as it should. The ECU adjusts fuel according to airflow, running lower boost will reduce power, but it will not cause the engine to run rich.

I have had a dawes valve and took it out again because it increased my fuel consumption by about a litre per hundred km.
The truck certainly was nicer to drive with it, but I was also a bit concerned about the fast spool up (which could be corrected with a needle valve), but I didn't want to fit another gadget.
I also monitored the vacuum solenoid and noticed that it rarely lets the turbo work with the vanes fully closed, so I thought it was better to put up with a bit of boost fluctuations and get the lower fuel consumption.
The other issue I had was losing clutch vacuum really fast, which does not happen with the standard setup (not an issue with autos).
So you do have boost fall off during EGR conditions???

I could care about 1L per 100 personally.

As for the vacuum if you have a series 3+ manual then it no longer has a vac tank, very easy to put one in. As for a needle valve being a 'gadget' is about the simplest piece of equipment ever built.
 

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Hi,
Mine is a 2001 with about 120,000 on it. It does have the vacuum tank. Contrary to what many people believe, when cruising at around 100 with very light throttle the boost goes highest, around 13 to 14 psi in my car (higher before I shimmed the lever on the turbo). This is actually when the EGR valve is OPEN, hence people go into limp mode when the EGR is blocked. When you accelerate, the boost usually drops and that is when the EGR shuts and the ECU reduces the boost.
The ECU pulls the lever on the turbo hard up to create maximum back pressure and force more exhaust gas through to the intake via the open EGR valve.
There are 2 main conditions when EGR takes place, firstly at idle, second at light throttle cruising when the rpm is below 3000.
 

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ZD30 Out - L77 In!
nissan patrol
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Hi,
Mine is a 2001 with about 120,000 on it. It does have the vacuum tank. Contrary to what many people believe, when cruising at around 100 with very light throttle the boost goes highest, around 13 to 14 psi in my car (higher before I shimmed the lever on the turbo). This is actually when the EGR valve is OPEN, hence people go into limp mode when the EGR is blocked. When you accelerate, the boost usually drops and that is when the EGR shuts and the ECU reduces the boost.
The ECU pulls the lever on the turbo hard up to create maximum back pressure and force more exhaust gas through to the intake via the open EGR valve.
There are 2 main conditions when EGR takes place, firstly at idle, second at light throttle cruising when the rpm is below 3000.
Hi hhl,

I agree with most of that and in general it is the correct theory, but unlike earlier or conventional EGR control systems the ZD30 in the Patrol does allow maximum EGR under load. Not full throttle, but under considerable load.

It increases boost under light load conditions for a lesser amount of EGR which as you say can put the engine into limp mode, but MAXIMUM EGR is only available under load and to achieve that, the ECU must reduce boost.

Believe me, I thought it was done as you said, but after testing the stepper motor voltages, it became apparent that EGR was still there under load.
I did this because I couldn’t find any reference to EGR control in the manual, but it’s apparent in the RD28 specs and the ZD30 Navara specs that boost is reduced for maximum EGR.

If you look at this table for the RD28, it clearly show the EGR control valve closes to allow maximum EGR. This has exactly the same effect as reducing boost on our VNT ZD30 turbo’s. This table was coppied from the RD28 manual.

 
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